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Chromatographic analysis of diesel exhaust indicates a number of low molecular weight hydrocarbons, below C6. Using reactivity index as a criterion, much of the diesel exhaust reactivity can be attributed to ethylene and propylene caused by the thermal decomposition of the fuel. Hydrocarbons in the C4-C7 range, including high relative reactivity olefins, are generally low in volume concentration and therefore contribute little to the overall exhaust reactivity. Hydrocarbons, in terms of parts per million carbon above C7 are low in present diesel engine designs, so individual volume concentrations are generally fractional parts per million. Reactivity per horsepower-hour from diesel engine exhaust is less than that from the one small industrial gasoline engine tested by the heavy-duty truck diesel engine cycle.

TESTS on two series of diesel engines were run. The first group, consisting of four engines, had the stroke changed only, while the second group had the stroke/bore ratio changed and the displacement held constant. Results of the tests indicate that the longer stroke engines had more power, higher torque, and lower fuel consumption. Friction was high for the short-stroke engines at low speeds and for the longest stroke engine at high speeds. Theoretical analysis indicates that the optimum stroke/bore ratio for best performance may vary as the compression ratio and bore diameter are changed.

AFTERCOOLING, coupled with higher pressure turbocharging can increase vehicle engine output. The author thinks that it is possible to anticipate diesel engines being run with compressors supplying air at pressure ratios higher than 2/1. Density ratio is the most important consideration in increasing pressure ratio, since the engine's output is dependent upon weight rather than volume of air supplied. Because the density of the compressed air is dependent upon its temperature at any pressure level, cooling the air after compression results in density increases. This paper describes various methods of after-cooling which increase engine output and fuel economy.

Two high specific output diesel engines designed for the Military -- the LVDS-1100 and LDS-750 engines, which are of V-8 and 5-cyl in-line configuration, respectively -- were developed by Caterpillar Tractor Co. under contract with U.S. Army Tank Automotive Center at Detroit Arsenal. This paper covers the development work, also sponsored by ATAC, required to adapt these engines for operation using regular grade gasoline in addition to the diesel and CIE fuels for which they were originally designed. Test techniques used, a description of some interesting combustion systems tried, and data obtained with the selected arrangement are included. The engine has excellent performance and starting characteristics with any of the three fuels.

After reviewing the present state of diesel engine design art as applied to vehicle applications, the paper analyzes future application requirements and outlines possible paths of engine development. In general, future requirements demand engines of higher output, lighter weight, better fuel economy, and smoke-free operation. A better understanding of vehicle load demands and careful matching of engine and drive-line will be required. Reference to extensive recent research developments shows that the diesel engine industry will be prepared to meet this challenge to provide the customer the best possible engine in terms of return on his investment.

Diesel engine exhaust emission characteristics vary considerably with the overall design of the combustion and fuel injection systems. Emission measurements were made on total hydrocarbons, nitrogen oxides, carbon monoxide, carbon dioxide, and smoke. The hydrocarbon measurements of the precombustion chamber engine are considerably lower than the direct injection engine. Less than five pounds of total hydrocarbons per 1000 gal of fuel are produced at rated conditions by all precombustion chamber engines studied. Precombustion chamber engines produce smaller quantities of the oxides of nitrogen when compared to direct injection engines. All diesels produced low carbon monoxide emissions. A novel technique for qualitative and quantitative evaluation of diesel exhaust odors is introduced. Exhaust odor intensity from the precombustion chamber engine is much less than that from the direct injection engine.

A system has been developed that provides real-time measurement of heavy-duty diesel engine particulates emitted during the EPA transient emission test cycle. This is accomplished by measuring the opacity of the exhaust/air mixture in an EPA type dilution tunnel with a light extinction opacity meter. Simultaneously, the temperature in the dilution tunnel is measured, and the ratio of the dilution tunnel temperature to a standard temperature is used to correct the opacity signal to standard conditions. The outstanding features of the system are that it produces a continuous record of when particulates were generated during the 20-minute transient cycle and that particulate cycle results are available immediately upon completion of the transient cycle without the requirement of conditioning and weighing filters. Results to date indicate correlation of the opacity-particulate monitor measured particulates to gravimetrically determined particulates to be within 10% for specific engines.

A cooperative research program has been completed evaluating the impact of fuel composition (volatility, aromatics and sulfur) on the combustion and emissions performance of a Caterpillar 3406B turbo-charged diesel engine, which is representative of diesel truck engines of the late 1980s. Tests included both steady-state and transient operation measuring regulated and unregulated emissions. The fuel set was blended using only commercially available refinery stocks typical of those which could be considered for use in distillate fuel. The compositions of the blends were selected so that direct measurements of the individual effects of 10% and 90% distillation temperatures, aromatic content, and sulfur content could be made independently. Engine combustion performance data indicated that all fuels operated satisfactorily; aromatic content was as high as 50% and cetane number as low as 39. Further, the cetane number did not predict the engine measured ignition delay in this program.